U.S. patent application number 17/246300 was filed with the patent office on 2022-06-30 for package for millimeter wave molecular clock.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Hassan Omar Ali, Juan Alejandro Herbsommer, Nikita Mahjabeen, Meysam Moallem.
Application Number | 20220209779 17/246300 |
Document ID | / |
Family ID | 1000005608075 |
Filed Date | 2022-06-30 |
United States Patent
Application |
20220209779 |
Kind Code |
A1 |
Herbsommer; Juan Alejandro ;
et al. |
June 30, 2022 |
PACKAGE FOR MILLIMETER WAVE MOLECULAR CLOCK
Abstract
In a described example, an apparatus includes: a package
substrate having a device side surface and a board side surface
opposite the device side surface; a physics cell mounted on the
device side surface having a first end and a second end; a first
opening extending through the package substrate and lined with a
conductor, aligned with the first end; a second opening extending
through the package substrate and lined with the conductor, aligned
with the second end; a millimeter wave transmitter module on the
board side, having a millimeter wave transfer structure including a
transmission line coupled to an antenna aligned with the first
opening; and a millimeter wave receiver module mounted on the board
side surface of the package substrate and having a millimeter wave
transfer structure including a transmission line coupled to an
antenna for receiving millimeter wave signals, aligned with the
second opening.
Inventors: |
Herbsommer; Juan Alejandro;
(Allen, TX) ; Mahjabeen; Nikita; (Richardson,
TX) ; Ali; Hassan Omar; (Murphy, TX) ;
Moallem; Meysam; (Plano, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
1000005608075 |
Appl. No.: |
17/246300 |
Filed: |
April 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
63133231 |
Dec 31, 2020 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 1/12 20130101; H03L
7/26 20130101; H05K 1/0243 20130101; H01P 3/003 20130101; H01Q
1/2283 20130101 |
International
Class: |
H03L 7/26 20060101
H03L007/26; H01P 3/00 20060101 H01P003/00; H05K 1/02 20060101
H05K001/02; G06F 1/12 20060101 G06F001/12; H01Q 1/22 20060101
H01Q001/22 |
Claims
1. An apparatus, comprising: a package substrate having a device
side surface and a board side surface opposite the device side
surface; a physics cell mounted on the device side surface of the
package substrate and having a first end and a second end; a first
opening extending through the package substrate and lined with a
conductor, the first opening aligned with the first end of the
physics cell; a second opening extending through the package
substrate and lined with the conductor, the second opening aligned
with the second end of the physics cell; a millimeter wave
transmitter module mounted on the board side surface of the package
substrate, having a millimeter wave transfer structure including a
transmission line e coupled to an antenna configured to transmit
millimeter wave signals aligned with the first opening; and a
millimeter wave receiver module mounted on the board side surface
of the package substrate and having a millimeter wave transfer
structure including a transmission line coupled to an antenna for
receiving millimeter wave signals from the physics cell, and
aligned with the second opening.
2. The apparatus of claim 1, wherein the transmission line in the
millimeter wave transmitter module comprises one selected from a
coplanar waveguide, a grounded coplanar waveguide, a microstrip,
and a stripline.
3. The apparatus of claim 1, wherein the physics cell comprises a
gas chamber containing a dipolar gas.
4. The apparatus of claim 3, wherein the dipolar gas is oxygen
carbon sulfide (OCS) gas.
5. The apparatus of claim 3, wherein the dipolar gas is a gas that
is one selected from oxygen carbon sulfide (OCS), water vapor,
hydrogen chloride (HCL), hydrogen cyanide (HCN), and acetonitrile
(CH.sub.3CN).
6. The apparatus of claim 4, wherein the OCS dipolar gas has a
series of discrete quantum rotational frequencies including a
quantum rotational frequency of 121.62 GHz +/-10%.
7. The apparatus of claim 1, wherein the first opening and the
second opening are rectangular in cross section and have a width
and length of approximately 1 millimeters and approximately 2
millimeters, respectively.
8. The apparatus of claim 1, wherein the package substrate
comprises a material that is one selected from FR4, BT resin,
ceramic, plastic, epoxy, fiberglass, glass reinforced epoxy
laminate, paper based laminate, and semiconductor substrates.
9. The apparatus of claim 1, wherein the package substrate
comprises FR4, and the conductor lining the first and second
openings comprises copper or copper alloys.
10. The apparatus of claim 1, wherein the package substrate has a
thickness between 1 millimeters and 5 millimeters.
11. The apparatus of claim 1, and further comprising ball grid
array terminals on the board side surface of the package
substrate.
12. The apparatus of claim 1, wherein the millimeter wave
transmitter module further comprises: a millimeter wave transmitter
integrated circuit mounted on a printed circuit board, the printed
circuit board having a top ground plane on a top surface facing the
package substrate, a coplanar waveguide on a first conductor level
within the printed circuit board coupled to the millimeter wave
transmitter integrated circuit, a bottom ground plane formed on
another conductor level within the printed circuit board positioned
beneath the first conductor level and the coplanar waveguide, and
vias extending through dielectric material of the printed circuit
board and coupling the top ground plane and the bottom ground
plane, the vias spaced from the coplanar waveguide.
13. The apparatus of claim 12, wherein the millimeter wave
transmitter module further comprises an opening in the top ground
plane, the coplanar waveguide ending in an antenna positioned
within the opening, the antenna configured to transfer millimeter
wave signals from the coplanar waveguide through the opening in the
top ground plane through air, and to the first opening in the
package substrate.
14. The apparatus of claim 13, wherein the millimeter wave
transmitter module is coupled to the package substrate by a
plurality of solder balls spaced from one another that surround the
opening in the top ground plane, the solder balls attached to the
bottom surface of the package substrate by solder joints.
15. The apparatus of claim 13, wherein the opening in the top
ground plane of the millimeter wave transmitter module is aligned
with the first opening in the package substrate.
16. The apparatus of claim 1, wherein the millimeter wave receiver
module further comprises: a receiver printed circuit board having
an integrated circuit for receiving millimeter wave signals mounted
thereon, and having a top ground plane on a top surface, a coplanar
waveguide formed on a conductive layer within the printed circuit
board, and a bottom ground plane on a conductive layer beneath the
coplanar waveguide, the bottom ground plane and the top ground
plane coupled together by conductive vias that extend from the top
ground plane to the bottom ground plane through dielectric layers
in the printed circuit board and spaced from the coplanar
waveguide.
17. The apparatus of claim 16, wherein the coplanar waveguide is
coupled between a receiver opening in the top ground plane and the
millimeter wave integrated circuit, the coplanar waveguide having a
probe in the receiver opening in the top ground plane of the
printed circuit board that is aligned with the second opening in
the package substrate.
18. The apparatus of claim 17, wherein the receiver printed circuit
board is mounted to the board side surface of the package substrate
by solder balls.
19. The apparatus of claim 17 wherein the receiver printed circuit
board is mounted to the board side surface of the package substrate
by solder bumps.
20. The apparatus of claim 19, wherein the receiver printed circuit
board has at least three conductor layers spaced by dielectric
material.
21. The apparatus of claim 1, wherein the millimeter wave signal
has a frequency of 121.62 GHz +/-10%.
22. The apparatus of claim 3, wherein the dipolar gas is OCS gas,
and the millimeter wave signal has a frequency that is one selected
from: 109.46 GHz +/-10%; 121.62 GHz +/-10%; and 133.78 GHz
+/-10%.
23. A system, comprising: a millimeter wave clock module comprising
a physics cell with a gas chamber containing a dipolar oxygen
carbon sulfide (OCS) gas with a quantum rotational frequency of
greater than 109 GHz; a processor configured to control a clock
generator coupled to the millimeter wave clock module, and to
detect an amplitude signal from the millimeter wave clock module,
the processor controlling the clock generator using the amplitude
signal to lock a clock signal to the quantum rotational frequency
of the millimeter wave clock module; and a clock output signal that
the processor synchronizes to the clock generator, the clock output
signal synchronized to the quantum rotational frequency of the
millimeter wave clock module.
24. The system of claim 23, wherein the millimeter wave clock
module further comprises: a physics cell comprising the dipolar gas
in a gas chamber in a semiconductor substrate, the physics cell
having a first end configured to receive millimeter wave signals,
and a second end configured to transmit millimeter wave signals; a
package substrate having the physics cell mounted on a device side
surface and having a board side surface opposite the device side
surface; a first opening through the package substrate aligned with
the first end of the physics cell, the first opening configured to
transfer millimeter wave frequency signals to the gas chamber of
the physics cell; a second opening through the package substrate
aligned with the second end of the physics cell, the second opening
configured to transfer millimeter wave frequency signals from the
physics cell; a millimeter wave transmitter module mounted to the
package substrate on the board side surface, the millimeter wave
transmitter module having a transmitter integrated circuit coupled
to a transmission line and configured to transmit a millimeter wave
frequency signal to the physics cell; a millimeter waver receiver
module mounted to the package substrate on the board side surface,
the millimeter wave receiver coupled to a transmission line and
configured to receive millimeter wave signals from the physics
cell; and ball grid array terminals for the millimeter wave clock
module on the board side surface.
25. A method, comprising: transmitting millimeter wave signals at
an expected quantum rotational frequency from an antenna on a
millimeter wave transmitter module through air to a physics cell
comprising a sealed gas chamber containing a dipolar gas; receiving
the millimeter wave signals from the physics cell at an antenna in
a millimeter wave receiver module; determining a signal strength of
the received millimeter wave signals in the millimeter wave
receiver module; adjusting the transmitted millimeter wave signals;
and determining a quantum rotational frequency by detecting the
frequency of the transmitted millimeter wave signals when the
signal energy received from the physics cell in the millimeter wave
receiver module is at a minimum signal energy.
26. The method of claim 25, wherein the dipolar gas is one selected
from one selected from oxygen carbon sulfide (OCS), water vapor,
hydrogen chloride (HCL), hydrogen cyanide (HCN), and acetonitrile
(CH.sub.3CN).
27. The method of claim 26, wherein the dipolar gas is OCS.
28. The method of claim 27, wherein the transmitted millimeter wave
signal is at a frequency between 120 GHz and 122 GHz.
29. The method of claim 25, wherein the transmitted millimeter wave
signal is 121.62 GHz +/-10%.
30. The method of claim 25, wherein the transmitted millimeter wave
signal is at a frequency of between 109 GHz and 134 GHz.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to U.S.
Provisional Application No. 63/133,231, filed Dec. 31, 2020 which
is hereby incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] This relates generally to packaging electronic devices, and
more particularly to packaging semiconductor devices and a physics
cell in a millimeter wave molecular clock module.
BACKGROUND
[0003] Increasingly, highly accurate and stable clocks are needed
for applications such as navigation and ranging, autonomous vehicle
control, and location services on devices including portable and
handheld devices. A physics cell includes a dipolar gas that
exhibits quantum rotational transitions. The physics cell can be
used to form a reference signal for a clock. The physics cell
includes the dipolar gas in a sealed gas chamber. Electromagnetic
energy in the form of a millimeter wave frequency signal, in an
example a signal of over 100 GHz, is transmitted to the physics
cell by a millimeter wave transmitter, and remaining signal energy
is received from the physics cell by a millimeter wave receiver.
The dipolar gas in the physics cell absorbs maximum energy at
quantized frequencies which cause a molecular rotational
transition. The transmitted signal frequency can be adjusted until
a molecular rotational transition is detected, the energy
absorption of the molecular rotation transition can be detected as
a drop in amplitude of the remaining energy received from the
physics cell. The transmitted signal frequency can be locked to the
quantized molecular rotation frequency. Because the quantized
molecular rotation frequency is highly stable over temperature and
over time, the locked transmitted frequency signal can be used as a
stable reference for generating a clock signal or a reference
frequency signal. A cost effective, robust and reliable package for
the millimeter wave molecular clock module is needed.
SUMMARY
[0004] In a described example, an apparatus includes: a package
substrate having a device side surface and a board side surface
opposite the device side surface; a physics cell mounted on the
device side surface of the package substrate and having a first end
and a second end; a first opening extending through the package
substrate and lined with a conductor, the first opening aligned
with the first end of the physics cell; a second opening extending
through the package substrate and lined with the conductor, the
second opening aligned with the second end of the physics cell; a
millimeter wave transmitter module mounted on the board side
surface of the package substrate, having a millimeter wave transfer
structure including a transmission line e coupled to an antenna
configured to transmit millimeter wave signals aligned with the
first opening; and a millimeter wave receiver module mounted on the
board side surface of the package substrate and having a millimeter
wave transfer structure including a transmission line coupled to an
antenna for receiving millimeter wave signals from the physics
cell, and aligned with the second opening.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram of an arrangement for a molecular
clock system.
[0006] FIG. 2A is a cross section of a package arrangement for
millimeter wave molecular clock module, FIG. 2B illustrates in a
cross sectional view a portion of a molecular clock system
including the package of FIG. 2A on a printed circuit board.
[0007] FIG. 3A illustrates in a cross sectional view a physics cell
for use with an arrangement; FIG. 3B illustrates in an alternative
arrangement a physics cell; FIG. 3C is a plan view of a physics
cell for use with the arrangements.
[0008] FIG. 4A illustrates in a graph the absorption frequencies of
an OCS gas cell having quantum rotational transitions; FIG. 4B
illustrates in a graph an example of absorption of a signal at a
quantum frequency.
[0009] FIGS. 5A-5B illustrate in a plan view and a cross section,
respectively, a package substrate for use with the
arrangements.
[0010] FIG. 6 illustrates, in a cross sectional view, a portion of
an arrangement including a physics cell mounted on a package
substrate.
[0011] FIGS. 7A-7D illustrate, in a cross sectional view, a close
up top view, and in further cross sectional views, portions of a
millimeter wave module for use with the arrangements.
[0012] FIG. 8 illustrates, in a projection view, a physics cell for
use with the arrangements.
[0013] FIGS. 9A-9B illustrate, in a side view and an end view, a
physics cell, a package substrate and millimeter wave modules in a
molecular clock module package of the arrangements.
[0014] FIG. 10 illustrates, in a flow diagram, a method
arrangement.
DETAILED DESCRIPTION
[0015] Corresponding numerals and symbols in the different figures
generally refer to corresponding parts, unless otherwise indicated.
The figures are not necessarily drawn to scale.
[0016] Elements are described herein as "coupled." As used herein,
the term "coupled" includes elements that are directly connected,
and elements that are electrically connected even with intervening
elements or wires are coupled.
[0017] The term "semiconductor die" is used herein. As used herein,
a semiconductor die can be a discrete semiconductor device such as
a bipolar transistor, a few discrete devices such as a pair of
power FET switches fabricated together on a single semiconductor
die, or a semiconductor die can be an integrated circuit with
multiple semiconductor devices such as the multiple capacitors in
an A/D converter. The semiconductor die can include passive devices
such as resistors, inductors, filters, or active devices such as
transistors. The semiconductor die can be an integrated circuit
with hundreds or thousands of transistors coupled to form a
functional circuit, for example a microprocessor or memory device.
The semiconductor die can be a passive device such as a sensor,
example sensors include photocells, transducers, and charge coupled
devices (CCDs), or can be a micro electro-mechanical system (MEMS)
device, such as a digital micromirror device (DMD).
[0018] The term "packaged electronic device" is used herein. A
packaged electronic device has at least one semiconductor die and
has a package body that protects and covers the semiconductor
device die. In some arrangements, multiple semiconductor dies can
be packaged together. For example, a power metal oxide
semiconductor (MOS) field effect transistor (FET) semiconductor
device die and a logic semiconductor device die (such as a gate
driver die or controller device die) can be packaged together to
from a single packaged electronic device. Additional components
such as physics cells, and other passives can be included in the
packaged electronic device. The semiconductor device die can be
mounted to a substrate that provides conductive leads, a portion of
the conductive leads form the terminals for the packaged electronic
device. The semiconductor die can be mounted to the substrate with
an active device surface facing away from the substrate and a
backside surface facing and mounted to the substrate.
Alternatively, the semiconductor device die can be flip-chip
mounted with the active surface facing the substrate surface, and
the semiconductor device die mounted to the leads of the substrate
by conductive columns or solder balls. The packaged electronic
device can have a package body formed by a thermoset epoxy resin in
a molding process, or by the use of epoxy, plastics, or resins that
are liquid at room temperature and are subsequently cured. The
package body may provide a hermetic package for the packaged
electronic device. The package body may be formed in a mold using
an encapsulation process, however, a portion of the leads of the
substrate are not covered during encapsulation, these exposed lead
portions provide the exposed terminals for the packaged electronic
device. The package body can be a metal shell or cover that
protects a device. Protective fillers such as low modulus material
can be used to protect the device.
[0019] The term "package substrate" is used herein. A package
substrate is a substrate arranged to receive a semiconductor die or
device and to support the semiconductor die or device in a
completed semiconductor package. Package substrates include
conductive lead frames, which can be formed from copper, aluminum,
steel and alloys such as Alloy 42 and copper alloy. The lead frames
can include a die pad for mounting the semiconductor die, and
conductive leads arranged proximate to the die pad for coupling to
bond pads on the semiconductor die using wire bonds, ribbon bonds,
or other conductors. The lead frames can be provided in strips or
arrays. Dies can be placed on the strips or arrays, the dies placed
on a die pad for each packaged device, and die attach or die
adhesive can be used to mount the dies to the lead frame die pads.
Wire bonds can couple bond pads on the semiconductor dies to the
leads of the lead frames. After the wire bonds are in place, a
portion of the substrate, the die, and at least a portion of the
die pad can be covered with a protective material such as a mold
compound.
[0020] Alternative package substrates include pre-molded lead
frames (PMLF) and molded interconnect substrates (MIS) for
receiving semiconductor dies. In one example, a MIS package
substrate is referred to as a "routable lead frame" or RLF. These
substrates can include dielectrics such as liquid crystal polymer
(LCP) or mold compound and can include one or more layers of
conductive portions in the dielectrics. The lead frames can include
plated, stamped and partially etched lead frames, in a partially
etched lead frame, two levels of metal can be formed by etching a
pattern from one side of the metal lead frame, and then from the
other side, to form full thickness and partial thickness portions,
and in some areas, all of the metal can be etched to form openings
through the partial etch lead frames. Repeated plating and
patterning can form multiple layers of conductors spaced by
dielectrics, and conductive vias connecting the conductor layers
through the dielectrics, the dielectrics can be mold compound. The
package substrate can also be tape-based and film-based substrates
carrying conductors; ceramic substrates, laminate substrates with
multiple layers of conductors and insulator layers; and printed
circuit board substrates of ceramic, fiberglass or resin, or glass
reinforced epoxy substrates such as FR4. In an example arrangement,
a package substrate of FR4 is used to mount a physics cell on a
first surface, and millimeter wave transmitter and receiver modules
are mounted on a second surface. Additional integrated circuits can
be mounted to the package substrate.
[0021] The term "millimeter wave signal" is used herein. Millimeter
wave signals have a frequency of between 30 GHz and 300 GHz. In
example arrangements, frequencies of greater than 100 GHz, for
example about 121 GHz or 133 GHz, are used to stimulate a physics
cell. In the arrangements, a millimeter wave transmitter module is
used, this module includes an integrated circuit that transmits
millimeter wave signals. A millimeter wave receiver module is used
in the arrangements, this module includes an integrated circuit
that receives millimeter wave signals. In the arrangements, a
frequency corresponding to a molecular rotation transition
frequency is referred to. In an example, the frequency for a
dipolar gas is 121.62 GHz. The molecular rotation frequencies for a
dipolar gas are physical constants. However, in the arrangements a
signal transmitted at a frequency transitions different materials
and traverses dielectric materials and air. Some variation in the
observed or transmitted frequency can occur, due to the materials
used in the arrangements, so that a normal variance of +/-10% may
be measured. In this description, when a particular frequency is
described, a variance of +/-10% is included, so that a molecular
rotational frequency of 121.62 GHz means 121.62 GHz +/-10%; and
similar variance is included in other described frequencies.
[0022] The term "physics cell" is used herein. A physics cell is a
cell which exhibits a physical constant. In the arrangements, a
dipolar gas physics cell has quantized molecular rotation. In
response to RF signals applied at one of a series of discrete
frequencies, the molecules in the dipolar gas physics cell absorb
the energy and transition from a first rotational state to a second
rotational state. When energy at other frequencies away from the
discrete quantized frequencies are applied to the physics cell, the
molecules will not transition and the energy is not absorbed.
Because the energy is almost completely absorbed by the cell at
certain frequencies that correspond to quantized molecular
rotational transitions, a receiver can detect when the transmitted
frequency is at a quantization frequency for the cell, and a system
can lock to the transmitted frequency. The quantized rotational
frequencies correspond to a physical constant and are highly stable
over time and over temperature, so that a stable constant frequency
reference can be obtained by use of the physics cell.
[0023] In the arrangements, a package substrate has a physics cell
mounted on a device side surface and millimeter wave transmitter
module and a millimeter wave receiver module mounted on an opposing
board side surface. A portion of the package substrate and the
physics cell can be covered with a shell, dielectric, shield or lid
to protect the physics cell. The millimeter wave transmitter module
and the millimeter wave receiver module include millimeter wave
integrated circuits mounted on high performance, high frequency
circuit board substrates. The millimeter wave transmitter module
and millimeter wave receiver module are mounted on a board side
surface of the package substrate opposite the device side surface.
Openings extending through the package substrate act as millimeter
wave coupling elements, and operate as vertical waveguides. A first
opening in the package substrate is arranged to receive a gigahertz
frequency interrogation signal from the millimeter wave transmitter
module. The first opening is lined with a conductor and forms a
vertical waveguide, in an example the waveguide is sized to form a
rectangular waveguide. The dipolar gas cell has an iris to receive
energy at one end of the gas chamber, which receives the
interrogation signal with high insertion loss and low reflectivity.
At an opposite end of the dipolar gas cell, a second iris that
transmits the remaining signal energy is coupled to a second
rectangular opening in the package substrate, this second opening
is also a vertical opening lined with a conductor and sized to form
a rectangular waveguide. The millimeter wave receiver module is
also provided on a high performance circuit board mounted on the
board side surface of the package substrate and includes a signal
probe on the end of a coplanar waveguide coupled to the second
opening in the package substrate. The package substrate is, in one
example, a fire resistant glass fiber reinforced epoxy, such as
FR4. Other substrate materials can be used for the package
substrate including ceramic and BT resin substrate materials. The
package substrate is not required to be a high performance
substrate, as the millimeter wave signals traverse openings
extending through the package substrate, and the millimeter wave
signals are not coupled to any traces within the dielectric
materials of the package substrate. Use of low frequency substrate
materials for the package substrate reduces cost for the package
substrate and the molecular clock system. The arrangements provide
a cost effective module for use in a molecular clock system, which
has been shown in simulations to be highly stable over a wide
temperature range.
[0024] FIG. 1 illustrates in a block diagram a molecular clock
system 100. Module 101, which is a packaged molecular clock module
of the arrangements, includes a physics cell 103, which in an
example arrangement includes a dipolar gas in a sealed chamber, the
dipolar gas can be an OCS (oxygen carbon sulfide) or
carbonylsulfide, gas. The dipolar gas exhibits quantum molecular
rotation so that when a signal of a frequency at a discrete
rotational frequency is used to stimulate the gas in the physics
cell, a quantum molecular rotation occurs that can be observed.
Other dipolar gasses can be used, including the OCS, water vapor,
hydrogen cyanide (HCN), hydrogen chloride (HCL), and acetonitrile
(CH.sub.3CN). The transmitted signal can then be used as a
reference frequency, and the system can be locked to the quantized
molecular rotation frequency of the physics cell in a control loop.
In an example arrangement the frequency used is about 121.62 GHz, a
molecular rotational frequency for OCS gas, but other transitions
at other quantum rotation frequencies may be used. For example a
second quantum rotation frequency for the OCS cell is at about
133.78 GHz.
[0025] A transmitter die 105 on a transmitter module is used to
provide a millimeter wave interrogation signal to the physics cell
103. A receiver die 107 on a receiver module is coupled to receive
the millimeter wave signal from the physics cell 103. The clock
module 101 is coupled to an analog-to-digital converter (ADC) 109
which samples the analog signal from the clock module 101 and
outputs a digital signal corresponding to the analog signal,
indicating the amplitude or magnitude of the analog signal. A
microcontroller 112 performs a control loop using, for example,
proportional integral derivative (PID) control. The microcontroller
112 tunes a clock generated by controlling a fractional N circuit
116. The fractional N circuit 116 includes a PLL and a signal
synthesizer and provides two outputs, one is a 10 MHz clock signal
to be used as an output signal for system 100, which is the stable
clock signal generated by the system, the other is a 320 MHz signal
to be used in a feedback loop. An oscillator 114 provides a raw
clock, for example a 630 MHz clock, to the fractional-N circuit
116, other raw clock input signals can be used. In an example this
oscillator can be a bulk acoustic wave (BAW) device, other
oscillators can be used. The fractional N circuit 116 has control
inputs that allow the microcontroller 112 to adjust an output clock
generated from the raw clock signal, and thus tune and lock the
control loop. In this example arrangement, a second fractional N
circuit 118 is shown receiving the 320 MHz clock and outputting a
reference signal of 10.135 GHz, in another example an output can be
11.1487 GHz. The reference signal from the fractional N device 119
is input to module 101 and is used by the transmitter die 105 to
generate the interrogation signal, for example of 121.62 GHz, by an
up multiplier ".times.12". While two Frac-N devices are shown in
the example of FIG. 1, in other arrangements a single Frac-N device
can be used. In some arrangements the BAW oscillator 114 can be
within the clock module 101.
[0026] In operation, the system 100 outputs a stable reference
clock signal of 10 MHz using the physics cell 103 to develop a
stable frequency reference used for generating the clock signal.
The transmitter die 105 sends an interrogation signal near an
expected quantum rotational frequency to the physics cell 103. The
remaining signal output from the physics cell 103 is received by
the millimeter wave receiver die 107, which outputs the power or
amplitude of the remaining signal, and the output signal is
filtered and conditioned and output to the ADC 109. A digital
signal corresponding to the magnitude of the output signal from 101
is then input to microcontroller 112 for use in the PID control
tracking loop. When the interrogation millimeter wave signal from
the transmitter die 105 matches the quantum rotational frequency of
the dipolar gas physics cell, the dipolar gas physics cell will
absorb most of the energy, and the output signal into the
millimeter receiver die 107 will be at an amplitude minimum. The
microcontroller 112 can adjust the frequency output by fractional N
circuit 116 until the minimum amplitude corresponding to the
quantized rotational transition is observed, and when that is
achieved, the microcontroller 112 can lock the circuit to the
reference frequency of physics cell 103.
[0027] FIG. 2A illustrates in a cross sectional view a packaged
millimeter wave clock module 101 of the arrangements. In FIG. 2A a
physics cell 103 is mounted on a device side surface of a package
substrate 131. A gas chamber 111 is shown in the cross section with
two ends exposed, the gas chamber is continuous in the physics cell
103 which can be formed in a semiconductor substrate. The gas
chamber 111 is sealed by glass bonded to the semiconductor
substrate on two surfaces, and is lined on all sides of the gas
chamber with a conductor such as gold. Other conductors of noble
metals can be used to line the gas chamber. Other conductors can be
used, and may be coated with anti-corrosion layers to ensure the
gas in the chamber does not react with the conductors. Copper with
additional coatings can be used. A millimeter wave transmitter
module 113 is mounted on a board side surface of the package
substrate 131, and transmitter die 105 is mounted on the module
113. A millimeter wave coupling structure 133 is formed between the
millimeter wave transmitter module 113 and the physic cell 103. A
millimeter wave receiver module 115 is mounted on the board side
surface of the package substrate 131, and carries millimeter wave
receiver integrated circuit 107. A millimeter wave receiver
structure 135 couples the physics cell 103 to the millimeter wave
receiver module 115. Terminals 161 for the package 101 are formed
on the board side surface of the package substrate 131, so that the
package 101 can be mounted to a system board. The terminals 161 can
be ball grid array terminals such as solder balls, solder pillars,
copper pillar pumps, copper columns, solder columns, stud bumps or
other ball grid array connections. A lid 151 covers the physics
cell 103 and the device side surface of the package substrate 131,
and can a metal, for example. The lid 151 can form an RF shield.
The lid 151 can be of other materials that will protect the physics
cell, and can be replaced by an overmolded dielectric such as a
mold compound, resin, epoxy, or plastic. Low modulus material can
be used to reduce stress on the physics cell 103 in addition to a
metal lid 151 or overmolded material used to cover the physics cell
103.
[0028] FIG. 2B illustrates, in another cross section, a portion of
a system 100 mounted on a system printed circuit board (PCB) 120.
The components external to the packaged clock module 101 are shown
mounted to the PCB 120, for example the fractional N circuits 116,
119, the microcontroller 112, a power circuit 117. The packaged
clock module 101 is shown in the cross section and includes the
physics cell 103, a package substrate 131, the millimeter wave
transmitter module 113 with transmitter die 105, and the millimeter
wave receiver module 115 with receiver die 107. Terminals 161 mount
the packaged module 101 to the PCB 120.
[0029] In FIGS. 2A-2B, the package substrate 131, which can be an
FR-4 substrate, supports the physics cell 103 and the millimeter
wave transmitter and receiver modules 113, 115. The package
substrate 131 has a transmitter coupling structure 133 and a
receiver coupling structure 135. These two coupling structures are
formed using openings in the package substrate 131 that are lined
with a conductor, such as a plated copper, and are shaped to form
waveguides that provide a vertical millimeter signal connection
between the transmitter module 113 and one end of the physics cell
103, and another vertical connection between the opposite end of
the physics cell 103 and the receiver module 115. By using
inexpensive substrate materials and arranging the openings to act
as rectangular waveguides, the package substrate 131 provides a
cost effective package solution for the clock module 101. Further,
in the arrangements the clock module 101 with an FR4 package
substrate has been shown to be extremely stable over temperature
changes. Packaged clock module 101 provides a set of devices in one
component for use in making a clock system, increasing integration
and ease of use, and reducing area needed on the system board.
[0030] FIG. 3A illustrates in a cross sectional view the physics
cell 103. A substrate 301 includes a gas cell 111 with a tubular,
polygonal or circular cross section that is lined with a conductor
(not shown for clarity of illustration). In one example process,
two wafers are used to form substrate 301. Each wafer has glass
substrate bonded to it in a wafer bonding process. One half of the
chamber is etched as a cavity pattern into each wafer. The cavities
are metallized with the conductor, for example, gold. The two
wafers are placed face to face, the gas is introduced, and an AuIn
wafer bond process is used to complete the chambers, trapping the
gas in the chambers. The individual physics cells on the wafers are
separated from the wafers in a singulation process. In FIG. 3A, the
two die portions 3011, 3012 are bonded at the dashed line 3014 to
form the substrate 301. Glass is used, for example to form a top
305 and bottom 307 layer. A low pressure dipolar gas, in the
arrangements OCS gas, is contained in the gas chamber 111 of
physics cell 103. Iris openings 321, 323 are formed at opposite
ends of the physics cell to receive and transmit the millimeter
wave interrogation signals. These openings are made in the
conductor layer (not shown) to allow the millimeter wave signals to
enter and exit the gas chamber 111.
[0031] A process for forming a sealed gas cell with molecular
rotation is described in U.S. Pat. No. 9,529,334, titled
"ROTATIONAL TRANSITION BASED CLOCK, ROTATIONAL SPECTROSCOPY CELL,
AND METHOD OF MAKING SAME", which is hereby incorporated herein by
reference in its entirety. The physics cell 103 can be made using
semiconductor process technology. A first die portion 3011 and a
second die portion 3012 are formed using silicon etch on two wafers
to make a cavity into a silicon substrate, for example, and the two
portions are bonded face to face using AuIn wafer bonding
(indicated by the dashed line 3014) to form gas chamber 111.
Because wet etching of silicon using an anisotropic etch, for
example TMAH wet etch, produces a trench with sloping sides, the
polygonal shape shown in FIG. 3A for the gas chamber 111 is
obtained. If a different silicon etch process is used, for example
a dry reactive ion etch (DRIE) process, the trenches in the two
dies may have more or less vertical sidewalls and the gas chamber
can have a square or rectangular shape, such as is shown for an
alternative shaped physics cell 331 as shown in a cross section in
FIG. 3B, when the two dies 3311 and 3312 are bonded face to face as
indicated by the dashed line 3314. A rectangular gas cell 311 is
then formed. The gas chambers 111, 311 shown in FIGS. 3A and 3B in
cross section with two ends exposed, but are a continuous chamber
plated with a conductor. Two openings are formed in the conductor
at the two ends of the gas chamber. The gas chamber is designed
with dimensions that are determined to provide efficient
transmission of the millimeter wave signals from a first end of the
gas chamber to a second end of the gas chamber.
[0032] The gas chamber is shaped and sized to act as a waveguide.
In an example, when the OCS gas is used and the selected resonant
frequency is about 121 GHz as is further described below, the gas
chamber 111 can be dimensioned similar to rectangular waveguide
WR8, which has a band of operation from 70 GHz to 140 GHz, and has
dimensions of about 2 millimeters.times.1 millimeter in cross
section. By sizing the gas chamber 111 or 311 appropriately for the
frequency signals being used, the mode of propagation can be a
single transverse electric (TE) mode, making the transfer of energy
through the gas chamber most efficient. For example, when the
frequency of the signals being applied to the gas chamber are about
121 GHz, a transverse electric propagation mode of TE.sub.10 is
desired. Further the transmission through the gas chamber should be
confined to a single transverse electric mode ("monomode") to avoid
losses by mode conversion. By sizing the gas chamber appropriately,
and by designing the dimensions of other elements of the system to
make efficient transmission at transmitted frequencies, a system
with high insertion loss and low reflective loss from the
transmitting millimeter wave integrated circuit to the receiving
millimeter wave integrated circuit is achieved. The length of the
gas chamber 111 affects the magnitude or "depth" of the absorption
response. When the quantized frequency signal is applied to the
physics cell, the dipolar gas will absorb the energy and transition
from a first rotational state to a second rotational state. When
other frequencies are applied, the signal will not be absorbed by
the gas chamber and most of the energy will be received by the
receiver. To increase the signal to noise ratio (SNR) and the
quality of the response, the gas chamber 1 should be made as long
as is practicable for a given package substrate area. In the
example arrangements illustrated here, a serpentine shape is used
for the gas chamber to lengthen it on the substrate. In an
alternative arrangement, the gas chamber can be made a "U" shape.
In example arrangements, the length can vary from end to end from
about 10 millimeters to 150 millimeters for an OCS gas cell, with a
longer cell providing better SNR than a shorter cell.
[0033] As shown in FIG. 3A, the gas chamber 111 has an "iris"
opening 321, 323 at each end where the conductive liner is opened
to allow signals to enter, and exit, the gas chamber. A metal
pattern on the glass surface (not shown, see FIG. 3C) can provide a
shield surrounding the iris opening at each end.
[0034] FIG. 3C illustrates the physics cell 103 in a plan view.
Substrate 301 is shown with the tubular gas chamber 111 extending
from a first coupler 341 at a first end and having a second coupler
343 at a second end. The couplers are positioned around the iris
openings 321, 323 in the conductor lining the tubular gas chamber
111 and are configured to receive, and transmit, millimeter wave
energy into the dipolar gas within the gas chamber 111.
[0035] FIG. 4A illustrates the absorption frequency spectrum for
OCS gas over a range of GHz frequencies from less than 60 GHz to
above 180 GHz. The molecular rotational frequencies are quantized
at discrete frequencies, about 12 GHz apart from one another. The
absorption is plotted on the vertical axis while frequency is
plotted on the horizontal axis. Referring to FIG. 1, as signal
absorption increases in the physics cell, the remaining signal that
will be output to the receiver by the physics cell decreases,
further as can be seen in the graph in FIG. 4, the absorption is
quantized. By applying an interrogation signal near one of the
quantum rotational levels, and by then tuning the interrogation
signal, the quantum rotational frequency can be used to lock a
signal at a known frequency.
[0036] Use of the dipolar gas cell has several advantages. Unlike
some other atomic clock cells which are stimulated with optical
energy and require temperature control to remain stable, such as a
precise heating element, the dipolar gas cell is stable over
temperature, reducing the need to tightly control the cell
temperature using heaters or other added circuitry. Unlike
optically stimulated clock cells, in the arrangements no optical
transducers are needed. In example arrangements, a quantum
frequency 401 of about 121.62 GHz was used, although it can be seen
from examining FIG. 4A that other quantum frequencies may also be
used. A useful alternative would be the next adjacent higher
quantum frequency, of 133.78 GHz. Another useful alternative would
be the next lower quantum frequency, of 109.46 GHz. Because the
wavelength of a 121.62 GHz signal, in air, is about 2 millimeters,
this frequency is particularly useful in the arrangements as the
available dimensions of the various components relative to the
wavelength make design of an efficient and cost effective transmit
and receive path feasible. Note that the wavelength of the
millimeter wave signals in a low-k dielectric material (such as in
a high performance substrate) will be less than in air, for
example, 900 microns or less at 121.62 GHz.
[0037] There are design trade-offs that need to be made in
determining the dimensions of the gas chamber, the size and shapes
of the openings in the package substrate, and the design of the
millimeter wave transmitter module, and the corresponding
millimeter wave receiver module. As can be seen in FIG. 4A, as
frequency increases, the magnitude of the response (amplitude or
signal strength) at the quantized rotation frequencies also
increases. Detecting the absorption frequency is clearly enhanced
by a stronger response. However, as frequency is increased above
100 GHz and even further such as 180 GHz, the availability of cost
effective transmitter and receiver integrated circuits is reduced.
If a frequency above the Fmax cut off limit for CMOS technology
integrated circuits is selected, the cost of the system will
increase, as the integrated circuits will need to be of more
expensive technologies, such as GaAs, which can operate at higher
frequency. The dimensions of the various features of the
arrangements are also related to the wavelengths of the signals
used. A signal of 121 GHz has a wavelength, in air, of about 2.47
millimeters. The size of the openings in the package substrate, the
cross sectional dimensions of the gas chamber, and the design of
the millimeter wave transmitter module and the millimeter wave
receiver module, are all impacted by the frequency and the
wavelength of the signals. Simulations including the various
elements can be used to insure the system has high insertion loss
between the transmitting integrated circuit and the receiving
integrated circuit, and low reflective loss, for the frequencies
selected. When a 121 GHz signal is used, the gas chamber and the
openings in the package substrate can be arranged similar in
dimensions to a WR8 rectangular waveguide, which has a useful
frequency bandwidth from about 90 GHz to about 140GHz. This
waveguide has a width of about 2 millimeters and a length of about
1 millimeter in cross section, which are useful sizes for the
package substrate and physics cell of the arrangements. Higher
frequency signals will have correspondingly smaller wavelengths, in
contrast lower frequency signals will have larger wavelengths. In
selecting the dipolar gas, the rotational frequency to be used, and
dimensions for the various elements of the arrangements,
simulations can be performed to ensure the module will have the
desired performance. The selection of the millimeter wave
transmitter and receiver integrated circuits is also determined, in
part, by the frequency of the signals being used.
[0038] FIG. 4B illustrates in a graph an example frequency response
showing an amplitude minimum for an OCS dipolar gas cell in
response to a quantized rotational frequency signal. The rotation
frequency Fr causes the molecules in the gas cell to absorb the
energy, using the signal energy to transition from a first
rotational state to a second rotational state, so that the
remaining energy output from the gas cell is at a minimum; as shown
in FIG. 4B, the magnitude of the remaining signal drops sharply at
the rotational frequency Fr. The millimeter wave receiver and
processor (see FIG. 1) can then be used to detect the rotational
frequency, and lock the frequency to the rotational frequency of
the gas in the physics cell. A highly stable clock signal can be
generated using the transmitted signal as a reference.
[0039] While OCS is a useful dipolar gas for the example
arrangements, other gasses that exhibit quantized rotation can be
used. The choice of the gas can be determined considering several
factors, including the quantized spectrum frequencies available,
whether the gas is corrosive or reacts with metal such as the
conductor liner of the gas cell, which may reduce the volume of
available molecules over time (for example water vapor can be
consumed in an oxidation reaction with copper); whether the gas is
a stable molecule over time; whether the gas is safe to humans or
animals if it should escape the gas cell into the environment; and
whether the gas is safe to use in production of the gas cells.
Availability and cost of the gas are also considered. The
dimensions of the openings in the substrate, the cross sectional
area of the gas chamber, the length of the gas chamber and other
dimensions can also be impacted by the choice of the gas, because
the rotational frequency will change. As described above, the
choice of the rotational frequency used changes the wavelength of
the signals and impacts the dimensions of the various elements.
[0040] FIG. 5A illustrates, in a plan view, an example package
substrate 131 for use in an arrangement. Openings 141, 143 are used
to form vertical waveguide structures, along with additional
components described below. Conductor material 145, which can be a
copper plated material, gold plated material, or other conductor,
lines the openings 141, 143. Substrate 131 may have additional
conductors and traces formed to route signals, or power, to the
millimeter wave modules, as shown in FIG. 1 above. None of the
millimeter wave signals are routed in traces formed in the package
substrate 131, making the use of a lower cost, low frequency
substrate material possible. Instead the millimeter wave signals
traverse the openings 141, 143 which act as millimeter wave
couplers, or as vertical waveguides. In an example arrangement, the
first opening and the second opening are rectangular in cross
section and have a width and length of approximately 1 millimeters
and approximately 2 millimeters, respectively, in an example
arrangement when a transmitted frequency signal is about 121.62
GHz, a quantized rotational frequency for OCS gas. If the
frequencies used or the dipolar gas selected change, then other
opening sizes can be used to make efficient millimeter wave
transmission to and from the physics cell.
[0041] FIG. 5B is a cross sectional view of the package substrate
131 taken along the line B-B' in FIG. 5A, showing the openings 141,
143 extending through the package substrate 131, and having
conductor material 145 lining the openings. The openings and
conductor in the package substrate can be formed using printed
circuit board fabrication techniques, by laser drilling, etch or
stamping the openings and by plating the conductor liner 145. Note
that the plan view of FIG. 5A shows the openings 141, 143
positioned to correspond to the ends of the gas chamber of the
physics cell 103. When a different shaped physics cell is used in
an alternative arrangements, the positions of the openings 141, 143
will be moved in correspondence with the different shaped tubular
gas chamber. The dimensions of the package substrate will be
determined, in part, by the size of the physics cell. The physics
cell will have better SNR performance as longer lengths of the gas
chamber are used, so it may range from 10 millimeters to 150
millimeters in length. The package substrate to support these
physics cells can be from 12.times.12 millimeters squared, to about
25.times.25 millimeters squared. The package substrate can have a
thickness similar to substrates used for semiconductor devices, for
example, from 1 to 2.5 millimeters. Thicker substrates can also be
used.
[0042] FIG. 6 illustrates in a cross-sectional view a partial
assembly step of module 101. The package substrate 131 has the
physics cell 103 mounted on a device side surface, and a cover 151
is shown protecting the physics cell 103. Openings 141, 143 are
shown positioned in correspondence with the first and second ends
of the gas chamber 111. Openings 141, 143 will be used to transmit
and receive the millimeter wave signals to the physics cell
103.
[0043] FIG. 7A illustrates, in a cross sectional view, a millimeter
wave transmitter module 113 for use with the arrangements. In FIG.
7A, a transmitter die 105 is shown on a high performance, high
frequency substrate 703. In an example, a millimeter wave
compatible high frequency substrate from Shinko was used with four
levels of metal conductors in a dielectric material. Substrates
with more or fewer conductor levels can be used. Solder balls or
solder bump connections 711 are shown placed on the die side
surface of substrate 703. A top ground conductor layer 720 overlies
the surface of substrate 703. A coplanar waveguide structure 723 is
formed in a metal layer of the substrate 703 below the top ground
layer 720 and is coupled to the transmitter die 105 by a conductive
via or trace. This coplanar waveguide structure 723 is positioned
with an antenna end 721 placed in correspondence with an opening
141 in the package substrate 131 (see FIG. 2, for example) and will
transmit signals into that opening. A bottom ground plane 726 is
formed by a conductor 727 that is below the coplanar waveguide 723.
The bottom ground plane is beneath the coplanar waveguide and is
grounded and coupled to the top ground plane 720 by vias 731. These
vias surround the position where antenna 721 is positioned.
Additional vias 731 (not shown for clarity) will couple the top and
bottom ground planes together across substrate 703. Solder balls or
bumps 711 surround an opening in the top ground plane 720 over the
antenna 721, these solder bumps form a guide, similar to a
waveguide, for directing the millimeter wave signals from the
antenna upwards to the package substrate (see FIG. 2). In
additional alternative arrangements, instead of the coplanar
waveguide 723, other transmission line types can be used to couple
the millimeter wave transmitter integrated circuit 705 to an
antenna. For example, microstrip, stripline, and other coplanar
waveguides that are not grounded, or where the top ground plane is
omitted, can be used.
[0044] FIG. 7B shows in detail a close up, plan view of the
coplanar waveguide structure 723. Note in FIG. 7B, conductor layers
and vias are shown while the dielectric material is omitted for
clarity. An antenna 721 is positioned in a central opening in the
top ground plane 720, the antenna 721 is formed at the end of the
coplanar waveguide 723 in a level of metal, and the vias 731 are
arranged around the opening to act like a waveguide to guide the
signals vertically towards the package substrate 131 (not visible
in FIG. 7A-7B, see FIG. 2A). Ground plane 726 is beneath the
antenna 721 and the coplanar waveguide 723, and covers the bottom
of the opening in top ground plane 720. By using these features as
millimeter wave guide structures, a cost effective microwave
coupling between the millimeter wave transmitter module and the
package substrate is created. The millimeter wave transmitter die
105 implements functions such as the ".times.12" multiplier in FIG.
1, a power amplifier, sensors, and other circuit components needed
to condition and transmit the interrogation signal. Note that the
receiver module 115 in FIG. 1 is symmetrical to the transmitter
module 113 and the cross section of FIG. 7A, and the plan view of
the coplanar waveguide 713 of FIG. 7B, will apply to the millimeter
wave receiver module 113 as well.
[0045] FIGS. 7C-7D are cross sectional views of the substrate 703
of the millimeter wave transmitter module 113, used to illustrate
some additional elements. In FIG. 7C, a side view of a portion of
the coplanar waveguide 723 with the antenna 721 is shown. Top
ground plane 720 has an opening 741 that corresponds to the opening
141 in the package substrate (not shown). A spacing distance "D" is
shown between the coplanar waveguide 723 and the bottom ground
plane 726. The coplanar waveguide 723 and the top and bottom ground
planes 720, 726 are conductor layers and can be formed of copper,
for example.
[0046] FIG. 7D is an additional cross sectional view of the
coplanar waveguide looking towards the antenna 721. Top ground
plane 726 has an opening 741, and bottom ground 720 is formed in a
conductor layer beneath the coplanar waveguide and antenna 721,
which is a conductor layer, such as level 1, above the bottom
ground plane layer 720. The distance "D" is determined to increase
the efficiency of the transmission of the millimeter wave signals.
For a frequency of about 121 GHz, for example, the wavelength (in
air) is about 2.4 millimeters. The radiation lobes from the antenna
721 will be, initially, symmetric so that the signal radiates up
towards the opening 741, and down towards the ground plane 720. By
choosing the distance D correctly, a constructive interference
signal can be created by reflection so that an in-phase reflection
appears traveling upwards as oriented in FIGS. 3C, 3D and shifts
the radiation lobe from a symmetric pattern to an asymmetric
pattern with most of the energy traveling upwards; in FIGS. 7C, 7D
this is represented by the arrow. Assuming a reflection at the
bottom plane 726 shifts the signal by 212, the distance D should be
selected to be 214, so that the total phase shift for a signal
traveling down from the antenna 721 to the bottom ground 726 and
back to the antenna 721 is (.lamda./4+.lamda./2+.lamda./4)=.lamda..
When distance D is correctly determined, the reflected signal will
add to the signal traveling upwards from the antenna 721 in a
constructive interference pattern.
[0047] In the examples in FIGS. 7A-7D, coplanar waveguide is used
as a transmission line o couple the millimeter wave integrated
circuits to antennas. However, in alternative arrangements,
microstrip or stripline conductors can be used. The top ground
plane shown in the examples can be omitted, or changed. The shape
of the antenna shown is one example, other shapes can be used. High
frequency simulation tools can verify the efficiency of a proposed
design, and the design can be tuned to determine the correct value
for distance "D", for example.
[0048] FIG. 8 illustrates, in a projection view, details of one
example of a physics cell 103. As seen in FIG. 8, the physics cell
103 includes a serpentine gas chamber 111 that is lined with a
conductor such as gold. A receiver iris 343 is at one end of the
chamber, and a transmitter iris 341 is at the other end of the gas
chamber 111. The ends of the gas chamber 111 are positioned and
aligned with the openings in the package substrate 131 as shown
above.
[0049] FIGS. 9A and 9B illustrate, in a side view and an end view,
the module 101 including the millimeter wave transmit and receive
structures 133, 135.
[0050] In FIG. 9A, the physics cell 103 is shown with chamber 111
on a device side surface, facing away from a system board side
surface, of package substrate 131. The transmit structure 133
includes the opening 141 in the package substrate 131 and the
solder balls 711 between the board side surface of package
substrate 131 and the transmitter substrate 703, while the receive
structure 135 includes the opening 143 in the package substrate 131
that is coupled to one end of the chamber 801 of physics cell 103,
and the solder balls 711 that surround the waveguide (not visible)
on substrate 703. The millimeter wave transmitter module 113 is
shown in part coupled tot eh package substrate 131 by the solder
balls 711. These elements are shown in an end view in FIG. 9B.
[0051] The transmit structure 133 includes the opening 141 in the
package substrate 131, the solder balls 711 on the millimeter wave
transmitter module 113, the coplanar waveguide and antenna
structures shown in FIG. 7B, and an iris for receiving signals at
one end of the physics cell 103. The receive structure 135 is
symmetric, including an antenna at the opposite end of the physics
cell 103, the opening 143 in the package substrate 131, the solder
balls 711 on the receive substrate of the millimeter wave receive
module 115, and the coplanar waveguide and antenna for the receive
module. By use of these elements, a cost effective, and temperature
stable package is provided for the clock module including the
millimeter wave transmitter, the millimeter wave receiver, and the
dipolar gas physics cell.
[0052] The arrangements reflect several design features selected to
lower cost of the packaged module. The use of the millimeter wave
transmitter module and millimeter wave receiver module (113, 115)
requires a high frequency high performance substrate. These
substrates are relatively expensive and the arrangements are
designed to reduce the size of these modules as much as possible.
In contrast, the package substrate 131 can be selected from a
number of inexpensive, often used, widely available, low frequency
materials. The size of the package substrate needs to be as large
as needed to support the selected physics cell. For example,
12.times.12 mm.sup.2 to 25.times.25 mm.sup.2 substrates can be
used, the size increasing with the length of the gas chamber in the
physics cell.
[0053] Referring to FIG. 2A, it can be seen that the millimeter
wave receiver structure 135 and the millimeter wave transmitter
structure 133 include portions of the millimeter wave modules
including the coplanar waveguide and antennas, the vias, the solder
balls on the millimeter wave modules, the openings in the package
substrate, and the iris openings in the physics cell gas chamber.
All of these elements are designed together, and work together to
make efficient transmission of the millimeter wave signals to the
physics cell. Use of the openings in the package substrate to
transmit and receive the millimeter wave signals, without the use
of high frequency conductors and dielectrics in the package
substrate, reduces cost of the packaged clock module.
[0054] FIG. 10 illustrates in a flow diagram a method. In FIG. 10,
at step 1001, millimeter wave signals are transmitted from an
antenna through air into openings to a dipolar gas in a physics
cell mounted to a package substrate. At step 1003, millimeter wave
signals are received from the physics cell in a millimeter wave
receiver module. As described above, this module is also mounted to
the package substrate and receives signals at an antenna over the
air through an opening in the package substrate. At step 1005, the
receiver determines the strength of the signals received, for
example as shown in FIG. 1, a square law detector in a millimeter
wave integrated circuit can be used in a receiver. At step 1009,
the frequency of the transmitted signal is adjusted. This step can
be repeated to tune the circuitry if needed. At step 1011, a
frequency corresponding to a quantum molecular rotational frequency
is determined by detecting the frequency when the signal is
absorbed by the physics cell, as shown in FIG. 1, a minimum
amplitude may be detected.
[0055] Modifications are possible in the described arrangements,
and other alternative arrangements are possible within the scope of
the claims.
* * * * *